1. Field of Invention
This invention is related to high solids low viscosity coating compositions and more particularly to coating compositions based on urea-formaldehyde crosslinking agents and low molecular weight polyols.
2. Prior Art
Coatings base on amino resins are well known in the art. In the book "Amino Resins", by J. F. Blais, Reinhold Publishing Co., N.Y., pp. 187-8, 1959, the use of amino resins in conjunction with alkyds is described. The amino resins are considered "in the nature of a modifying supplement" and are usually present as the minor component of the coating compositions.
In U.S. Pat. No. 2,794,008, issued May 28, 1957, to V. W. Ginsler, there are disclosed compositions which contain ester diol plasticizers for aminoplasts. Such compositions can contain up to 95% by weight of aminoplast but rely on the plasticizing effect of the mono-carboxylic acid ester moiety for practical utility. The nature of these compositions requires long baking schedules to obtain cured films.
U.S. Pat. No. 2,688,604, issued Sept. 7, 1954, to T. J. Suen, discloses molding compositions based on urea-formaldehyde resins and unsymmetrical diol ethers of glycerol and which can contain as little as 2% by weight the diol ethers. By the nature of the diol ether modifiers, however, one of the hydroxyl groups is secondary and therefore the crosslinking process is relatively slow.
British Pat. No. 748,913, published May 16, 1956, discloses a process for preparing solid urea-formaldehyde foams containing, among others, 10-35% by weight of polyethylene glycol having 3-50 oxyethylene groups. The emulsion systems utilized, however, are not useful as barrier coatings.